1. Field of the Invention
This invention relates generally to the field of magnetic memory disks for data storage. More specifically, it relates to a flexible disk with a metallic hub and to a method of manufacturing the same.
2. Description of the Prior Art
A floppy disk has a thin flexible substrate made of polyethylene teraphalate or similar material that is coated on one or both sides with a suitable magnetic oxide. The thickness of the substrate is about three thousandths of an inch. The disk is used as the data storage medium in a floppy disk unit. The disk has a central aperture that is adapted to receive a spindle for rotating the disk within a protective jacket. Openings are provided in the jacket for receiving the spindle, for enabling a read/write head access to the magnetic surface of the disk, and for enabling a photosensor to indicate to a control program the location of an index hole for determining the relative angular relationship between record data on the disk and the read/write head. A clamping device is positioned opposite the free end of the spindle for pressing the disk onto the rotating spindle in positive engagement to quickly bring the disk up to operating speed.
It is desirable to have the flexible disk concentrically mounted on the spindle, but manufacturing and mounting tolerances introduce some eccentricity. Furthermore, each time the disk is mounted on the spindle, the disk portion adjacent the central aperture is subjected to wear and damage that is cumulative. After several cycles of operation, the central aperture becomes eccentric relative to data tracks that ideally were concentric with the central aperture when recorded. Such eccentricity causes misalignment between the data tracks and the read/write head. When data is recorded on a disk that is mounted eccentrically to the spindle, the resulting data tracks are non-circular, and this causes reading errors during subsequent use of the disk.
While the afore-mentioned alignment problems cause errors for disks having a conventional number of data tracks per radial inch, these problems become more critical for the new micro-disks that have an increased track density. Some conventional disks had no reinforcement adjacent the central aperture, and the substrate material held up for the wear life of the disk. U.S. Pat. No. 4,052,750 of Barber, et al, shows a disk having an annular reinforcement member concentrically arranged adjacent the central mounting aperture, on one or both sides of the disk. The reinforcement member is cemented to the disk. The use of cement, glue or adhesives make the manufacturing somewhat cumbersome. There are problems of contamination and special care must be taken to maintain cleanliness. U.S. Pat. No. 3,729,720, of Darling, et al, shows a recording disk with a mounting hub in the form of two parts that are clamped on opposite sides of the disk by fingers extending from one part through the central aperture of the other part. When two parts are clamped together by crimping, quality control is a problem. Close tolerances are required to obtain the right clamping force. Thermoexpansion can jeopardize the clamping strength and allow the disk to work loose with no visible effect but resulting in recording errors.
U.S. Pat. No. 3,586,816, of Hagen, discloses a laser spot welding system and method for producing a series of microscopic spot welds in a specific array. U.S. Pat. No. 3,769,117, of Bowen, et al, and U.S. Pat. No. 3,868,490, of Jean-Phillippe Aeschlimann, et al, show further applications of laser welding.